1. Field of the Invention
The present invention relates in general to devices for sensing actuator operating signals in hydraulic systems and, more particularly, to a structural improvement in such an actuator operating signal sensor for hydraulic system having at least two actuators for not only sensing uni-actuator operating signals and multi-actuator operating signals, but also for discriminating between uni-actuator operating signals and multi-actuator operating signals.
2. Description of the Prior Art
Typically, the detection of fluid pressure in a directional control valve for an actuator of a hydraulic system is often used to determine whether the actuator's operation lever was handled to operate the actuator.
With reference to FIG. 1, there is shown a hydraulic system having a typical actuator operating signal sensor. As shown in the drawing, the hydraulic system includes two directional control valves 103a and 103b connected to their associated actuators 101a and 101b. Two auxiliary valves 105a and 105b are directly coupled to the control valves 103a and 103b respectively. The internal lines of the auxiliary valves 105a and 105b are opened or closed in accordance with positions of spools for their associated control valves 103a and 103b. A fluid line 107 extending from a hydraulic pump P to a return tank T passes the auxiliary valves 105a and 105b in a series. The internal lines of the auxiliary valves 105a and 105b are opened when the spools of the valves 103a and 103b are in their neutral positions, but opened when the spools of valves 103a and 103b are moved.
In order to sense operating signals from actuators 101a and 101b in the above hydraulic system, or to determine whether the operation levers for the actuators 101a and 101b were handled to operate the actuators, the pressures PA and PB at given points of the line 107, or at point A (between the pump P and the first auxiliary valve 105a) and at point B (between the first and second auxiliary valves 105a and 105b) are detected. That is, when the first actuator 101a is in operation by handling its associated operating lever, the pressure PA at point A will increase as the internal lines of the first auxiliary valve 105a are directly connected to the first control valve 103a are closed due to movement of the spool of the first control valve 103a. In the same manner, when the second actuator 101b is in operation by handling its associated operating lever, the pressure PB at point B will be increased as the internal lines of the second auxiliary valve 105b directly connected to the second control valve 103b are closed due to movement of the spool of the second control valve 103b.
The pressures PA and PB at points A and B in accordance with operational states of the actuators 101a and 101b are given in the following Table 1. In the following description and in Table 1 for the pressures PA and PB, the value "0" is a relatively lower value meaning that all of the internal lines of the auxiliary valves 105a and 105b are opened, while the value "1" is a relatively higher value meaning that all of the internal lines of the auxiliary valves 105a and 105b are closed.
TABLE 1 ______________________________________ 1 neutral position of 101a, 101b
= 0, PB = 0 2 exclusive operation of 101a
= 1, PB = 0 3 exclusive operation of 101b
= 1, PB = 1 4 operation of 101a, 101b
= 1, PB = 1 ______________________________________
1) In the case of neutral positions of the operating levers for both actuators 101a and 101b or non-operation of both actuators:
The internal lines of both auxiliary valves 105a and 105b are opened so that both pressures PA and PB have the value "0".
2) In the case of exclusive operation of the first actuator 101a:
The internal lines of the first auxiliary valve 105a are closed while the internal lines of the second auxiliary valve 105b are opened so that the pressures PA and PB have the value "1" and "0" respectively.
3) In the case of exclusive operation of the second actuator 101b:
The internal lines of the first auxiliary valve 105a are opened while the internal lines of the second auxiliary valve 105b are closed. However, both pressures PA and PB have the value "1" as closing of the Internal lines of the second valve 105b exerts influence upon both points A and B of the line 107.
4) In the case of simultaneous operation of both actuators 101a and 101b:
The internal lines of the both auxiliary valves 105a and 105b are closed so that both pressures PA and PB have the value "1".
In the above description for the hydraulic system having the typical actuator operating signal sensor, it is noted that the device can sense both the case of at least one actuator operating and the case of no actuators operatins, however, the device can not discriminate the case of exclusive operation of an actuator from the case of simultaneous operation of two actuators. That is, the typical device can not discriminate the case of exclusive operation of, for example, the second actuator 101b from the case of simultaneous operation of the two actuators 101a and 101b as both pressures PA and PB in the above two cases alike have the value "1" as shown in Table 1.